Electronics > Repair
Voltage Increase, failed component?
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shakalnokturn:

--- Quote from: ajp8868 on July 29, 2024, 06:04:47 pm ---Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

--- End quote ---

In my experience statistically (not exclusively) it's down stream from the regulator and should show as heat.
If it is the regulator by itself it should be even easier.
fzabkar:

--- Quote from: ajp8868 on July 29, 2024, 06:49:03 pm ---
--- Quote from: fzabkar on July 29, 2024, 06:31:12 pm ---
--- Quote from: ajp8868 on July 29, 2024, 06:04:47 pm ---Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

--- End quote ---

Being a linear regulator, there would be a 7V differential between input and output. A load current of 140mA would dissipate 1W in the regulator.

--- End quote ---

Meaning..?

--- End quote ---

I'm just saying that it doesn't take much current to heat up the regulator, so a warm regulator may be normal.
ajp8868:
So, I thought I'd made great progress. I found a shorted smd capacitor!

I couldn't find any 10uf caps on my donor boards so I went for a 5uf thinking it might not make much difference and might get it at least working.

Slight success.. I got the pan/tilt working!

However none of the other steppers are working now!!

Could it be that cap..? I've circled it on the attached image - could 5uf make that much difference??
ajp8868:

--- Quote from: fzabkar on July 30, 2024, 04:07:06 pm ---
--- Quote from: ajp8868 on July 29, 2024, 06:49:03 pm ---
--- Quote from: fzabkar on July 29, 2024, 06:31:12 pm ---
--- Quote from: ajp8868 on July 29, 2024, 06:04:47 pm ---Had another look and the lm7805 regulator seems to be getting very hot.. could this be a symptom of it failing and drawing too much current? Or is it more likely to be a failed component on the 5v rail?

Bearing in mind the 5v side is working perfectly

--- End quote ---

Being a linear regulator, there would be a 7V differential between input and output. A load current of 140mA would dissipate 1W in the regulator.

--- End quote ---

Meaning..?

--- End quote ---

I'm just saying that it doesn't take much current to heat up the regulator, so a warm regulator may be normal.

--- End quote ---

Ah that makes sense, yeah they both get hot, this one just gets a tad hotter. It's working though so wasn't the fault.
ajp8868:
So it seems that a 74HC04 has now blown which I believe is from me disconnecting a stepper driver while powered up... I'm not exactly sure of it's function but it definitely is controlling these steppers.

Swapped one from a working board and it seems to have sorted it (for a brief moment until I pulled a stepper driver while powered on again, which is how I know that was the cause of it blowing)

Ordered a couple of replacements and a new driver chip, so I'll keep you guys updated!
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